First of all everybody experience grief differently so some people even feeling realy sad would not cry on funeral.
And it is OK that you felt at peace - so no need for crying.
It is just that people do often judge other based on their own life motivation and experience (since thay do not know anything else) - so their thinking is that if they would not cry it would mean they didnt care for your dad - thereofre thay apply the same thinking at you.
also it was in history something that was “expected” - there ware even profesional crying woman (weeper) hired for funerals. So in past it was believerd it is necesarry to cry on funeral. so it was common to fake it just to do what was expected - it was seen as inapropriet to not to cry.
So your family can come from culture where this thinking is still common and they believe it is better to fake emotions to “fit in” or how to say.
If you are as you say strond emotinally and spiritually - there is no reason for you to doubt yourself and think that you migh be bad person. You know in heart who you really are.