1. I'm not playing 88 ovrpr for 70bb stacks against an unknown on that board... or likely any board except maybe if you had 88 + OESD or combo draw. You don't.
2. SB is still to act. Both of them could have pwnd right now with made straight and 99+. Lets also not forget two pair (67, 46?) and set.
3. You have 6 outs to improve (assuming someone isn't sitting on 89)... 2 8s and 4 5s. Anyone with two cards higher than 8 also has 6 outs to improve in a way that will crush you unless you hit your 1:4. So even if you're ahead now, I don't like the reverse implieds -- esp if SB comes in too as lottsa paint is in their range.
4. If I could have all the money back that I've lost to meh overpairs, I would have more money.
5. Goes without saying, but you have no fold equity as you ain't doing the pushing.
6. At this level, a push like this could be a lot of things. Yes, could be semi-thinking player protecting a good pair (or even two-pair or a set) by heavy handedly pricing out draws. I've also seen this exact same line with a made straight 'cause vill sucks at bet-sizing and/or thinks a big push like this will look bluffy and will get more callers.

thems my 2-cents... but I am a noobie and a nit