Possibly dust attack, but the amount spent on dust attack will be a lot less than 4 Euros and the attacker will send an amount that is the minimum funds that can be sent which poses a risk to your privacy.
My observation as well, 4€ is way too much for a dust attack as dust attacks constitutes amounts that have almost zero value.
Well, I can’t tell what might be the motive here but, it’s possible that something fishy might be the case since, the transaction is done without any plausible reason as per solicitation and probably, doesn’t constitute a region in it’s distribution.
Your reaction on the other hand would make all the difference. When you get such unsolicited coins in your wallet and it’s something that is been done to a whole other persons or wallet address, you have to watch it and tighten your security less, you lose everything.