Yes, it's a Matsumoku bass (good thing, most Hondos were Korean & not great quality) and yes, the bridge is bending as a result of 35-odd years of string tension - many Mat basses from this era have 3-point units made from cheese. They're not radiused, just rubbish, I'm afraid.
I have a Matsumoku-built Westbury Track 2 which had a very bendy bridge when I got it:
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Did a bit of research and this is a very common problem which turns up on lots of late 70s/early 80s Mats with these bridges.
I found a period-correct baseplate for mine, otherwise the simplest solution is to replace it with an Epiphone or compatible unit, which will fit, or to upgrade with a fully adjustable Hipshot or Babicz replacement.