The Ethiopian Government if not wanted would not allow the...

The Ethiopian Government if not wanted would not allow the Eritreans to help them. Eritrean territory on the border with Tigray region was occupied by the former Tigray/Ethiopia Government.

The new Eritrea friendly Government wants to return this Territory back to Eritrea. As an International Hague Border Commission had ruled years ago that this is illegally occupied land belonging to Eritrea. The Tigray local Government was an obstacle to this as they would not accept this and was entertaining sovereignty ideas from the central government in Ethiopia.

So if Eritreans were in Tigray then it was a) coordinated with the Ethiopian Government to support them, b) to return the land to Eritrean troops. You can’t call it a war it is more a battle or military operation in the same way you have it on the China/India, Pakistan/India or South-North Korea border.