Both notations are used online. Are they interchangeable? Is it even accurate to call it a "coin" in this respect?
Yes, they are interchangeable. The term I've heard foundation members use more often is token.
Most people however just say "iotas", "kiloiotas" (1000), "megaiotas" (1000000) and so on when they talk about a certain amount of tokens you have/you want to send/etc.
Since IOTA is not just the token but the whole foundation, network, ... you would use "token" or "coin" if you want to specifically refer to the cryptocurrency.
In general. Iota is neither a coin, nor a token.
Iota is more then just a Cryptocurrency for payment, like Bitcoin or Ethereum is, so it is not a simple coin. It is not a Token, because a token always depends on a coin, like erc20 tokens. Tokens do have a special usecase and iota does also have one. So if you want to be accurate, there is a new word needed.
Of course both words can be used and both terms are correct. Most of the time the word is used, which describes the usecase the speaker is referring to best. So you can see the intention of the speaker by focussing on his/her words.
Coin is the original notation for all cryptocurrency -- for example, bitcoin.
Tokens is used as a synonym for coins 99% of the time. The only slight distinction is that some people seem to refer to second layer cryptocurrencies, such as those that rely on Ethereum's smart contract layer or potentially in the future PEAQ tokens on IOTA, as tokens more frequently than coins.