It's quite common for games to have bugs or unintentional behavior when pressing left+right simultaneously. Super Mario Bros. is one example (as another commenter points out); another example is Super Metroid (for the SNES), which allows you to repeatedly wall jump in-place if you hold left+right: https://wiki.supermetroid.run/L+R_Walljumping

This sparked a mild controversy recently in the speedrunning community: L+R walljumping makes it possible to climb walls underwater without Gravity Suit or Hi-Jump Boots. Through the use of very esoteric and difficult speedrun tech, this enabled a runner to complete the game while collecting only 13% of available items, which would beat the previous low% record of 14% if left+right runs were allowed on the leaderboard: https://wiki.supermetroid.run/13%25_xCharge