Most people who post code-golf challenges never accept an answer, so people are more likely to compete in the challenge. (I personally don't see how the accepted mark would change which challenges you do/don't look at though, tbh.. But I can understand the reasoning of not accepting any answers at all.)
I myself accept answers after a few weeks however (and update when a shorter one is posted later on), so I can relate to your question. I have a few challenges where two or three answers have the same byte-count. Those I personally left without an accepted mark. And I sometimes check to see if anyone made a golf to their answer and there is now a single shortest one.
Most people who accept answers on code-golf challenges like us would accept the earliest one. So in the case of your challenge, the answers were posted at:
- Excel: October 1st, 2018 at 18:51:27
- MATL: October 1st, 2018 at 15:38:39
So in this case, the MATL answer would get the accepted check.
Alternatively, although I think your rep is currently to low for this feature, you could offer both answers a 50-bytes bounty to show your appreciation.
Whatever you choose is up to you. The general consent is to not accept code-golf challenges, and if you do, to accept the shortest one (and earliest posted in case of a tie), as the accepted answer in your linked meta-post also states:
If no tie-breakers are specified, or all specified tie-breakers are exhausted, the earliest answer wins. When determining which answer was earlier, the timestamp of the first valid edit which gave the current score counts.