Hello!
why "tslint.json" and "tsconfig.json" files are shown with TS icon?
Because of their relationship to TypeScript I decided to give them the TS icon. Do you think that it will be better to give them a normal JSON icon? Or what is the cause of your question?
Files may be related to typescript, but icon normally indicates file type, not relationship.
I tested other icons extensions as well as default icons, your icon set is the best, except this one issue, that confuses. When i want find "tsconfig.json" i suggesting that file has json type and i'm expect that it will be shown as json, not typescript...
Same, I also find this confusing. It's a JSON file. I have mutliple tslint rule configs and it's strange that only the one with a specific file name shows this way.
Here's a gif of this I recorded

Changed behavior for me. here is file location:
%UserProfile%.vscode\extensions\PKief.material-icon-theme-1.2.0\fileicons\material-icons.json
"fileNames" section is responsible to that behavior, small customization fixed issue, at least for me.
Alright, I changed it, tslint and tsconfig have the default JSON icon right now. The case described by @chrismbarr wasn't clear to me. I also noticed that I have the JSON icon for the eslint files and even for the jsconfig.json file, and so this will be the best solution.

Most helpful comment
Files may be related to typescript, but icon normally indicates file type, not relationship.
I tested other icons extensions as well as default icons, your icon set is the best, except this one issue, that confuses. When i want find "tsconfig.json" i suggesting that file has json type and i'm expect that it will be shown as json, not typescript...