One can get a false young age when using the method. And one can also get a false old age by doing so too.
A false young age will usually be of terrestrial deposits. And that would occur from incompetence. You know that creationists are more likely to be incompetent and not follow proper protocols than experts. The protocols that are used exist because contamination is a risk. And his sources clearly broke protocol because one clear part of protocol is to accurately record all aspects of sample collecting so that others can see that protocol was followed.
@SavedByTheLord cannot even demonstrate that a proper record was kept. That alone makes the dates worthless from a scientific viewpoint. For land based samples there are all sorts of ways that just a little C14 can be added to the sample. The first time that creationists tried to date materials that was done so by the source of their fossils. The source was not told what they were going to do with the samples so they were properly treated for shipping. Part of that is painting with shellac. This is not done so that a nice patina develops and that it looks all shiny and fossilly. No, it is done because it increases the odds that one will receive a fossil and not a box of sand. It protects the sample from the rigors of shipping. Shellac is a substance made from the excretions of lac bugs and has modern C14 in it. So of course that gives it a false young date. That with the calcite in the fossil (CaCO3) will give it a mix of new carbon and old carbon. The old carbon would have no C14 the new would have some and a date of younger than 50,000 years will arise.
For marine deposits the problem is contamination with old carbon. For example the sea water itself may be hundreds of years old if one is at a place of upwelling. Sea life tends to recycle carbon from several sources, existing shells on the sea floor. Incoming dissolved CaCO3 from limestone. There are all sorts of sources of old carbon that generally makes sea life incompatible with carbon dating. It is called "the reservoir effect". When Kent Hovind tried to claim that C14 didn't work he used an article that explained how and why it cannot be used on sea life. He ignored that it does work when done properly elsewhere. The article that he used was merely saying "don't use it for this sort of material and here is why". The stupid of Kent, it burns!
At any rate C14 dating is not as easy as some would think. Caution has to be used in acquiring material and the source that dates it needs to be informed of necessary details. It does not look as if the creationists did this at all.