A muḥkam Hadith is an accepted Hadith with no opposing Hadith of equal standing.
When the meanings of two Hadith appear to oppose each other, this is called taʿāruḍ (apparent conflict).
The prayer and charity report is an example of muḥkam: it has no opposing Hadith of equal standing. This is what the term concerns, not whether the wording is short or easy.