yes he prob was. i'm not sure if u remember, but there was a whole arc on impel down…so consider this (and this aint just to you, but for ppl who is doubting arlong's appearance in any form)
1. arlong is a big boss. he would haev been in level 5 minimum, and even possibly level 6, lets assume he was in lvl 6
2. we know that all level 6 prisoners were released. they fought each other and only thhe strongest would leave. we also know that blackbeard didn't take all of them, only a select few. arlong could have broken out. he can also swim.
3. there has been a 2 year leap. anything could have happened in those two years. however, i think we can all agree that arlong is not someone who would go into retirement, or would not open up a swordfish delicacy store. he most certainly have been doing something, either taking over territories, or trying to exact revenge on Luffy.
arlong was, in relation to the other level 6ers, nothing more than a speck of dirt. he was a small time captain in east fucking blue. there is NO WAY he would end up in level 6. bounty doesnt mean everything but it is a rough guide to where he'd end up (shown in the manga aswell - someone saying that over 100,000,000 end up in level 5) and his was a very small bounty indeed comparatively.
you are officially a retard if you think its viable for arlong to be in level 6. he got beaten by luffy waaaaay back at the start, the government wouldnt consider him a threat.