Learn English – Another phrase for “unsung hero”

The whole phrase is definitely not some idiom, it's just normal use of the idiomatic phrase in this specific context:

I can tell that [something]...

is equivalent to "I know that [something] is true"

"Things below" in this case means the listed statements. You could replace that statement in the linked question with "I know that:"

The asker asks this to avoid answers to contain informations he knows already, so he lists his current knowledge before asking questions that depend on it.

In this case, below (not bellow) means simply "listed under this statement", normal physical below as "located lower".

Consider synonyms of consistent, such as compatible and congruent; eg, “Results of experiment B were consistent / compatible / congruent with those of experiment A.” Also consider in accord with; eg, “In accord with predictions based on experiment A, experiment B showed that...”