IDK, I see weird claims like that from customers all the time! They see non-existent error messages with ridiculous texts. There's constantly weird inconsistencies like this in descriptions of real bugs.
I just assume that these people are very confused and not good at english.
Well, maybe he's a troll or maybe he's just confused or delusional, but either way I don't think the claim that google is banning people for using youtube-dl or newpipe should be taken seriously at this moment. I'm certainly not going to stop using youtube-dl.
I don't think the emailed explanation exists, and I don't think confusion can explain why he'd say it exists, which leads me to conclude he's lying.
(And really, if such bans were genuinely a threat, more than one person would be complaining about it happening. Tons of people use youtube-dl and newpipe (including many youtube creators who do commentary on other youtube videos) and there's this single guy claiming to have been banned for it. It doesn't pass my sniff test.)