Is it normal to be invited to boyfriends bonenkai?

To specify, not the actual 忘年会 itself, the nijikai after the bonenkai. His boss and coworkers apparently invited me, and it’s come up several times.

For context: he’s Japanese, I’m not, but works at an English speaking foreign company based in Japan.

Should I go? Is it weird? I’m not sure if he’s taking the standard courtesy invite the wrong way.

I don’t mind going but I haven’t seen this happen at my own bonenkais lol.