Check out his LinkedIn profile - https://www.linkedin.com/in/patrickshyu - from the projects he describes there, seems like he can back it up. And what's wrong with telling people you're an "ex googler/facebook"? If that's the experience you have to share, fair enough.

There's nothing wrong with telling people you're an "ex googler", but mentioning it whenever you can is quite... weird?

I mean from Youtuber that wants to get viewers perspective it's perfectly reasonable, but generally it looks not nice for me.

Here's a good starting point for understanding what's going on:

https://en.wikipedia.org/wiki/Running_gag

It's a running joke in the channel. "Hi welcome to my channel TechLead, with your host The TechLead who's an ex-google and now an ex-facebook tech lead"

I think it's tongue in cheek.

From what I can gather the guy is going in on satirical comedy. Specifically in the way we tend to evangelise these big tech companies and those who work for them.

Sometimes his delivery is so deadpan that I get an odious vibe from it. But it does seem that he’s not serious and is using his previous status as a part of the humour.

Some of his earlier videos did show him breaking down and laughing. He’s gotten good at maintaining his serious look after doing this for two years.

It's part of his comedy schtick. If you watch enough of his videos you realise how developed and deep his personality actually is.