In animated textures, currently it is “forward, random, pingpong, shuffle”
“forward” would be a little less confusing if it was changed to “sequential”.
Otherwise animated textures need to be set to both “forward” as well as “is reverse” to get them to play backwards.
Alternately you could remove the radial button “is reverse” from the node and make it one of the options from the dropdown “Forward, REVERSE, random, pingpong, shuffle”