I've seen it before, I played a random huge with 10 players with AI, 5v5, with only 88 GWs it gets cramped quickly, this time the random placements put 5 players against the other 5 in a rough semicircle with me bordering 1 ally and 2 enemies.
I pushed hard with LRFs and crippled one of the AIs so he ended up with only the HW and 1 roid, but the neighbouring AI was raiding me hard and defending the crippled AI so I had to SB up and fortify whilst I expanded/pushed else where.
I start scouting the frontlines after 10mins or so and the crippled AI built nothing but a fleet of scouts
Well, if you were LRF spamming scout fleets would actually be a pretty decent counter. Otherwise maybe he was short on resources?
As for the OP, while I haven't checked on the new difficulties, I've noticed some of the types of AI strongly prefer certain ship types. For example aggressive and economizer tend to like light frigates, while researchers will obviously get more advanced ships out. Sense you probably left the AI on random, this might be what happened.