Assuming we are talking United States Judicial System, Your Post is riddled with errors that could get any one following it massive monetary damages and Criminal prosecution with up to 1 year in jail.
IDK if you should even give illusion any credit because it seems like there would be a case to be made that they cant PROVE your renders came from HS.
In the United States, Lawsuits are Civil law, which unlike Criminal law where a case is decided beyond a reasonable doubt, civil Law is "A preponderance of the Evidence" or put simply who's story is more believable given the evidence presented.
It could be that your art style happens to look exactly like HS but you actually made them in blender lol.
And after making this statement under oath, Illusions lawyer will cross examine and ask you to show all the intermediate development files showing the stages of your work that any graphics artist makes. If you some how make a believable case that "your dog ate it". Their next question will be "How many thousands of hours did you spend producing that amount of content in Blender and how long it would take you to make it with Illusions software?
Saying "I spent 10,000 hours making this in blender even though I could have done it in under a 100 hours using their software", will likely piss the jury off at your blatant insult to there intelligence.
And lastly Lying under oath IS a criminal offense and can result in Jail Time as well as opening yourself to further civil action by illusion substantially increasing how much you will owe in Damages.
As to the original question I came here hoping to find out if any one can provide a a case of Illusion having filed a C&D or taken other legal action against a small developer for this since I haven't found any with a brief search. if they haven't taken action in the past, then baring pressure from an outside entity, such as the "RapeLay" incident, then I surmise that you should worry more about being struck by lighting on a sunny day. Even if they did the worst I can see is illusion filing a C&D, let alone paying thousands of dollars to sue what they likely see as "Some unknown geek so poor they can't even make the game using professional software." since they would have a tough time collecting enough damages to make it worth the cost.
Please note that this is a simplified explanation with dramatic moments added for effect. Real lawsuits tend to move slower than a Patreon developer milking his 3000 followers, and have less drama and suspense then a 1 star game on this site.