If you’ve enjoyed the salt that followed, why do you care if it’s bad manners or not? ECM being considered bad manners and the guy being mad aren’t two mutually exclusive things.
Lots of things in PVP can be considered bad manners; gatecamping, neutral logi, dropping supers on frigates etc. Yet those who do them don’t give a single ■■■■, and those who don’t are entitled to any kind of opinion they may have of them.
Also Hornet ECs aren’t really that good of a tactic. You are basically reducing your effective drone count from 20 to 10, making you a lot more susceptible to defanging and sacrificing damage type/speed variety. Once the Hornets roll their first jam attempts, if they fail they are out in the space doing nothing for 20 seconds, which is basically a 70% probability. During that 20 seconds an Enyo can reduce their number to 2 if not wipe them out entirely (ECs are squishy af), and the second jam attempt will be an even poorer excuse of what it was before. On top of that, now that the Enyo knows you only have 5 damage dealing drones, he may opt to just pop them and reduce your DPS to a sustainable level. You could try some shenanigans like releasing ECs and pulling immediately if they fail, but that’s still about 10 seconds where a significant chunk of your DPS is off the field.
Oh, also if the Hornets score their jams, you need to keep them in space so that the jam persists over the whole 20 seconds, during which time your DPS is from blasters only. Have fun.
TL;DR: Unless you enjoy PVP done in the framework of some sort of e-bushido, you have no reason to care. Aside from the fact that EC-300s in Ishkurs aren’t really good.