QR Codes might be encoded with a different algorithm
Every QR Code Generator uses different algorithms and also different encodings (Numeric, Alphanumeric, Byte Mode, Kanji Mode, ECI Mode) when creating a QR Code. Therefore, it is possible that different looking QR Codes can have the same URL or text information encoded.
QR Codes might be encoded with a different error correction level
Another possibility are different error correction levels (L, M, Q or H). The higher the error correction is set the bigger the QR Code gets.
The two QR Codes in the title image look different but have the same content. Scan each of them and you will see or create your own QR Code and set different error correction levels.