Line Etiquette in Tokyo?

Hi all, had an experience today in Tokyo and wanted to understand what the local etiquette is around lining up.

We queued up at a super popular restaurant Godaime Hanayama Udon Nihonbashi that always has a long line of people waiting. In front of us was a single suited guy who had already been waiting for at least 10-15 minutes.

Then suddenly a group of 10 people (tourists) showed up and took his place — turns out he was basically holding the spot for them (seemed like maybe a driver or assistant). This group also looked like they were rich with the brands that they were wearing and had assistants/maids accompanying them.

This obviously increased our wait time quite a bit, and the restaurant didn’t intervene when we pointed it out.

My partner got pretty upset and ended up confronting them, which turned into a an argument. Their stance was that it’s totally fine for one person to hold a place for a group of any size, and that if we had asked “nicely”, they might have let us and all others go ahead.

So now I’m curious — what’s actually considered proper line etiquette in Japan?

Is it generally acceptable for one person to queue and then have a large group join later? Or is this frowned upon but just tolerated?

Would appreciate any insight so we know what to expect (and how to handle it) next time.