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Retina, 19 bytes

Byte count assumes ISO 8859-1 encoding.

O`.+
Mm1`^(.+)¶\1
0

The input should be linefeed-separated. Output is 0 for falsy and 1 for truthy.

Try it online! (Slightly modified to support multiple space-separated test cases instead.)

Explanation

O`.+

Sort the lines in the input. If a prefix exists it will end up directly in front of the string which contains it.

Mm1`^(.+)¶\1

Try to match (M) a complete line which is also found at the beginning of the next line. The m activates multiline mode such that ^ matches line beginnings and the 1 ensures that we only count at most one match such that the output is 0 or 1.

0

To swap 0 and 1 in the result, we count the number of 0s.