Just to be clear, this is not QQ, just a question about how his ult works.

I was playing game against bots and Nunu bot started his ult. Both myself and a teammate silenced him, but it didn't interrupt his ult. He didn't have BV. Is this a glitch or does only hard cc stop Nunu's ult?

It's most likely a glitch, although to be totally honest Silence might not actually work on Nunu's ult because iirc it doesn't have a channel bar.

Probably a glitch though.

yes silence cancels Absolute Zero

yes there is a channel bar

yes it was a glitch

Same thing always seems to happen to me. I silence nunu, doesn't stop his ult.

I tried that before with a friend, with nunu and fiddle...
the silence didn't cancel his ulti, the fear did...
but, we tried that a couple of times... and the silence didn't cancel it...
but i'm pretty sure I have seen a silence cancelling his ulti... is kinda strange

I remember playing Taric a few times and stunning him during his ulti, just for it to not stop it. Had teammates *****ing at me nonstop and I kept trying but it kept not working.

nunubot surprised you with his immunity

baby Teemo