I don't remember Reno leaving, but I guess he could have sped ahead quickly after going all Roy Mustang vs. Lust on the Heartless that Creeper sent after them with lightning. 

Since they are low level as you mentioned in your post where Belle and Thomas fought them then they could have been instantly dispatched by Reno this way. 

Alright, ill edit my post to include Reno speeding ahead.