How to tell if a transaction is related to an NFT (erc721) transaction or not in etherscan

The ERC-721 standard defines Transfer event that has to be emitted with each token transfer, containing 3 topics:

• 1st indexed topic is the sender address
• 2nd indexed topic is the recipient address
• 3rd indexed topic is the token ID

The ERC-20 standard defines a very similar Transfer event, also with 3 topics. But the 3rd topic, representing the amount of transferred tokens, is not indexed.

So when you look at the event logs produced by this transaction, there are two Transfer events. Both of them have the 3rd topic non-indexed, meaning they are transferring ERC-20 tokens - not NFTs. If they were transferring NFTs, the 3rd topic would be indexed.