As long as the tile does not break under 250 pounds of pressure the tile is considered to be compliant with these standards.
Tile floor crackles.
Ceramic floor tiles especially larger tiles need an even distribution of mortar underneath them.
I also think the double wax ring on the toilet has failed as evidenced by the blistering paint in the ceiling board and recessed light below.
As a general rule tiles larger than 12x12 inches should have mortar applied to the back of the tile as well as the floor to help ensure adequate coverage.
However cracks wider than 1 8 inch will eventually transfer to the tile it.
Most tiles comply with astm c648 breaking strength standards.
Most tiles meet the 250 pound minimum.
Finally tile floors installed over a concrete subfloor are the most susceptible to cracking because the concrete itself is prone to cracking the geeksonhome article states.
In this test floor tiles are run through a machine that exerts loads on an unsupported 1 inch square area.
Voids in the mortar under the tile allow the tile to flex and crack.
Sometimes hairline cracks in tile floors are one of the first tell tale indications that soil or moisture is affecting a foundation.
In a case where cracking is minimal or has occurred in only a small number of tiles and or the floor is in a location where aesthetics don t matter to you the easiest most inexpensive solution is diy patching.
Generally hairline cracks in the concrete will not present an issue to the tile floor above.