Somalia is sick and tired of Eritrean arms being funneled to al-Shabaab terrorists. Eritrea is sick and tired “tired and sick” of being accused of funneling arms to al-Shabaab terrorists in Somalia. Somalis are probably sick and tired of being caught between arms smuggling in a country already awash with guns.
Eritrea certainly had made a practice of arming Somali insurgent groups to fight the Ethiopian forces occupying Somalia. This was not out of sympathy with the Somalis who detested this occupation, but rather to tie up the hands of the Ethiopian military, with whom Eritrea remains on tense terms over a border dispute. The Ethiopians, of course, have since departed Somalia, but it might still be in Eritrea’s interests to keep things roiling there.
As for Eritrea’s claims, that “ulterior motives” are behind Somalia’s accusations of Eritrean arms trafficking and that “western powers” are the ones responsible for Somalia’s internal problems, they sound pretty similar to the counter-attacks one might expect of a government accused of illegal arms shipments. Yes, Western countries have also been guilty of “meddling” in Somalia, but that does not make Eritrea’s influence — which, as a regional actor, could be considered much greater — any less damaging, “ulterior motives” or not.