Partition layout is a different level than the one on which the files with user (or system) data live. Partition schemes divide a block device, usually a hard drive, into several regions, which operating system kernel can use to support file systems, which in turn are used for hosting files.
When you resize a partition that already holds some file system, that file system's meta data may be changed. Emphasis on the "may" is important - resizing a partition doesn't mandate changing the file system - you can easily have a file system that uses less (or more) space than there is in a partition. If it uses less, all is fine, except for not being able to access the difference between the partition size and the file system boundary. The opposite case is where it gets problematic - the file system is using space that someone else might be claiming (the file system basically overlaps the subsequent partition). You can even have a file system that is completely unaligned with any partitions on a disk - but then again people usually don't do this kind of things.
That said, some programs (
parted being one) can try to resize the file system on a partition, provided they find it there and know how to do that - some file systems can only be grown.