Critical success on a natural 20 is a variant rule from an older edition of D&D.
In D&D 5e, rolling a natural 20 on an ability check, which includes Wisdom (Perception), is neither an automatic success nor an exceptional result. You either beat the check DC or not.
The rules for ability checks are defined in Player's Handbook, Chapter 7: Using Ability Scores, p.174:
As with other d20 rolls, apply bonuses and penalties, and compare the total to the DC. If the total equals or exceeds the DC, the ability check is a success—the creature overcomes the challenge at hand. Otherwise, it's a failure, which means the character makes no progress toward the objective or makes progress combined with a setback determined by the DM.
The DM in the linked video appears to be using a variant rule for critical success, which allows a natural 20 to gain an exceptional result.
The DM may have been inspired by two rules which appeared in Dungeons & Dragons 3.5's Dungeon Master's Guide (2003):
Critical Success or Failure (3.5 DMG p.34):
This D&D 3.5 variant rule allowed skill checks can roll a critical hit on a natural 20 the same way attacks can (thanks to mattdm for noting this variant). An example given by the book:
When using Search, the character discovers something that she otherwise could never have found (if anything is present to be found).
Degrees of Success (3.5 DMG p.32):
A standard rule in D&D 3.5 allowed an especially high roll to have even greater success. An example given by the book:
If the cleric beats the assassin's check result by 10 or more, he has achieved a greater success, and he gets the second answer. If he exceeds the assassin's check result by 20 or more, he has achieved a perfect success and he gets all the information—the third answer.