It's common to have plastic shavings in the bottom of the tank, or even the entire circle of the cut-out. Normally no problem, simply because the pump can't suck them up in most system (the pump suction intake is enough above the tank floor that it doesn't happen). Further, some systems include the optional strainer (screen) just ahead of the pump itself, designed to catch stuff like that as well as sand and grit that is often present in fresh water.
You wouldn't want that sort of stuff passing through the pump regularly cause it causes wear or possibly even internal damage, but tank installation shavings are pretty much a one-time thing. If that's what they are, they should have been sucked through long ago unless the former owner rarely used the pump or never ran the water level down to the bottom of the tank. It won't bother the water heater itself, but any place where there is a check valve, shut-off or bypass valve could get clogged. The toiler flush valve or ice maker solenoid valve, for example.
If you don't find a strainer at the entrance to the pump, I'd add one just to be sure. Or add an inline filter just after the pump, one that will filter all the water in the system, whether it comes from the tank or the city inlet. Make it a fairly good sized one so that the water flow rate is adequate for a good shower.
https://www.rvwaterfilterstore.com/
