Keeps saying "Expecting XNB, found """

[Julio8632]

Whenever I try unpacking a file, it says this:

C:\Users\insertmynamehere\Desktop>xnbcli.exe unpack ".\packed" ".\unpacked"
[INFO] Reading file "packed\Lex.xnb" ...
[ERROR] Filename: packed\Lex.xnb
XnbError: Invalid file magic found, expecting "XNB", found "▼"
at Xnb._validateHeader (C:\snapshot\xnbcli\app\Xnb\index.js:0:0)
at Xnb.load (C:\snapshot\xnbcli\app\Xnb\index.js:0:0)
at processUnpack (C:\snapshot\xnbcli\xnbcli.js:0:0)
at Walker.walker.on (C:\snapshot\xnbcli\xnbcli.js:0:0)
at Walker.emit (events.js:198:13)
at Object.emitSingleEvents [as emitNodeType] (C:\snapshot\xnbcli\node_modules\walk\lib\node-type-emitter.js:58:13)
at Walker._wLstatHandler (C:\snapshot\xnbcli\node_modules\walk\lib\walk.js:88:19)
at C:\snapshot\xnbcli\node_modules\walk\lib\walk.js:106:12
at FSReqWrap.oncomplete (fs.js:154:5)

Success 0
Fail 1

I saw a similar issue from a different person, I'm trying the same thing he/she was doing, extract a file from a game on steam, and turn it into a .png
I just don't understand how the .xnb file is "zipped". I can't extract the raw file any further, so how would I unzip it?