This type of semantic argument is meaningless. You can call it a credit, an incentive, a subsidy, a bonus, a rebate ..... Doesn't really matter. At the end of the day (... or year?), when comparing with buying an ICE car of the same price, your bank account has an extra $7,500, and the government has $7,500 less. You can call it whatever you want to call it; so I don't see what is there to argue about.
I think it's ideological. Some people don't like the idea of government influencing economy and therefore don't like to think of themselves as being influenced by government policy. So they view the tax policy of the EV tax credit as "keeping my money" vs. tax, energy, economic, national security government policy.