Because sometimes the situation is bad for your boss too, the company is in financial straits, miscommunication, {insert other extenuating circumstances}.
... but sometimes your boss really is just an asshole, liar, alcoholic, and/or a sociopath.
Never assume the later off the bat, but never completely discount the possibility either. Because it'll probably happen at least once in an average career.
So the difference doesn't really matter. You have a bad boss; take care of yourself first and don't let them push you around.
So? That's the boss's problem to deal with. You owe the company absolutely nothing beyond your contracted hours in exchange for your contracted salary.
I say this as an employer.
If your boss happens to be a cog in a broken machine, treating them like it's their fault isn't fair to them or you.
Of course, you can always quit (and usually should). But failing to determine root cause and mis-blaming your boss is about as useful as screaming at the gate attendant when your flight gets a weather delay.
And someone who by choice decides to be (or remains) a cog in the broken machine, specifically at the point where it requires being nasty to someone, is fully responsible for that action and its consequences.
(Labor advocacy programs help balance the scales a little, if only because your advocate is predisposed to believe you and help you navigate the options available to you. But they're fairly thin on the ground in the UK and the US.)
Didn't have the cash or energy to start it off and after 5 years I didn't want to go back to that bit of my life and kick it all off again. Plus he folded the company after a bit so chance I'd get anything were near zero.
It is one of the reasons I am so very suspicious of folks who diminish the value of labor protections. Most of us end up downrange of some shady stuff at least once.
I was doing on call support for a bunch of Linux machines. Literally it was him and me left because the moment I started the other two engineers bailed. One went to work packing salad because it was a better job (big warning!) and the other one had a breakdown.
So didn't get paid properly, argued mileage down to the mile, the clients and him constantly gave me verbal abuse over and over and I ended up working until 10pm some nights with my 9 month pregant wife at home on her own and virtually immobile due to a back problem.
So I get home one night after a tirade of abuse for the day and sent him an email saying "Fuck you I quit". Get a call about an hour later and he's drunk shouting abuse down the phone. This suddenly turns into undying love and care for me after the abuse wasn't working and he realised I couldn't be brow beat into coming back again. Then there's a thud which I assume was him falling off his chair. Never spoke to him again but the company folded about a year later.
So I sit down and I'm about £2000 down then on salary and expenses that were missing. I had £250 in the bank, £400 rent due a week later, wife about to have a baby and an empty fridge. So fuck it. I sold all the stock I still had of the company on ebay (back when you had to take photos and get them developed and scanned and futz with cheques which was hard work), broke even and scraped a first pay cheque at a job just before my credit card melted into a puddle.
It took 10 years to get out of the hole and back to normality. NEVER put up with this for a second. If anyone treats you like this RUIN THEM before they ruin you, your life, your relationships and everyone else they go near. I don't usually advocate this attitude but the damage and destruction that type of person leaves is immense.