I have been working alongside a more experience colleague, and he is more technically skilled than me. However, I was offered a promotion that I fee he deserves more than I do. Should I voice it out?

The person who make the decision has more information than you.

He chose to promote you based on information that you may not be aware of.

1) a better engineer does not mean he can be Chief of Engineer

2) The role may need other skills and not as much of technical skills.

I have promoted people with lacking technical skills but of greater valuable skills. Technical skills is but a small parcel.

When considering a promotion, usually the boss takes into account not just technical skills, but also other critical skills like people skills.

Depending on your organization, the promotion might come as your boss thinks you are ready to take on the next role and the responsibilities thus the offer of the promotion.

Yes, there are people who refuse promotions, either they are not ready for the new role or prefers other type of roles, or don't want to deal with people (e.g. being a team lead ), have family commitments and do not want the extra workload or already have personal plans etc...

This is what I will do if I were you:
Instead of having the question and guilt when accepting the promotion, you could consider having a heart talk with your boss in private or over a tea break setting if comfortable. Tell him you are very happy to receive the promotion and appreciate his acknowledgement of your work and efforts, however, you thought that another colleague has more experience or deeper technical skills than you and you actually feel bad about it. Perhaps he can enlighten you on why or how you edged out?
This can also be useful as you might learn something if they are willing to share their promotion criteria (also for your future promotions or honing your "identifying talent skills" assuming they did make the right decision).
I'm not too worried about boss judgement in this case, as it's not actually something bad or against integrity or against core values etc... Unless you know your boss is a narrow minded or highly narcissistic person.. then maybe not...

In some organizations, e.g. consulting, promotions are ongoing throughout the year and have to be justified across the same band, and some people are just suay not to have the right opportunities or projects to allow them to shine and be promoted. In this case, don't feel so bad for your own promotion... Their chance shall come soon..

Don't feel bad. He might have rejected promotion(s)? I know of colleagues who specifically inform their reporting officers that they do not want to be promoted because they don't want the extra responsibilities that usually come with promotions. Especially common for those with families. Also heard that some senior executives choose to stay in that job band and just get pay increment within the band because the range is really large. In fact it could actually overlap with the lower income range for the next job band, which is assistant manager.

If you're promoted, it means that your boss sees something in you. By voicing it out, you are effectively voicing your doubt over your boss's judgement. It doesn't reflect well on you, and your boss might even feel offended.