ABS question

Today was snowy, and I was climbing a steep hill in my Sable and part way up the ABS and (P)(!) brake lights came on. Now this hill is quite steep, and
fairly long (1/4 - 1/2 mile) and in order to get up, the front wheels were spinning the whole time (speedo reading 30 MPH, real speed probably 15MPH.)
Did the ABS light come just come on because the system was confused that the front wheels were turning twice as fast as the rear? Or could there be a problem? After I got to the top I shut the car off and started it and the lights cleared, and the ABS system functioned fine.
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