Is this called scamming?

scammers are 3 year olds that think being untrustworthy would help them in the real world

Back on topic, this is definitely a scam.While some types of scamming involve this, this isn't scamming in general. The dictionary definition of scamming is:a confidence game or other fraudulent scheme, especially for making a quick profit; swindle. Scamming in general is usually tricking someone to make a profit. Some types of scamming in gaming include:
Sharking (When you convince someone an item is worth more then it is to sell it to them)

Quickswitching (Usually used in steam trading, it's when you switch out a valuable item at the last moment to something that looks similar)

Le old paypal scam (Hurr durr gimme your diamonds/steam items/etc and I'll pay you, but then the scammer runs)

And simply, tricking people to make a profit like in this case. Scamming can get incredibly complex, and I would stay very careful on any case like this, in any game. I've made about 450$ profit using steam, and I've encountered pretty much every form of scamming (and lost about 70$ to a shark)

The items are diamond helmet (Protection 4 Respiration 3), diamond chestplate (unbreaking 1 or 2, thorn 2, protection 3), diamond pant (protection 4, thorn 2), diamond boot (protection 4) and my diamond sword named Legendary Cookie Sword (unbreaking 3, sharpness 5, fire aspect 2, knockback 2). He might be holding the items on his character because he log off just as i died.

why on earth would you trade that kind of gear? if i were you I would trade it to an honest person

Noveva, I have left signs on his/her/its island. Ill get back to you shortly

I was under the impression that the nether was free reign but if this happens then its scamming?

EDIT: I didn't think this was scamming but that player has done it to a few other players I know of because Im on skyblock a good amount of times to listen to people complain and ask questions but he has been doing this pvp take items things a lot so if we are going to punish him give him the full punishment.

Issue has been dealt with for now. Noveva, I am working my best to get your items back.

Johnnyc2010 was also a victim of him.