Scripture doesn’t say that Satan can read our minds, but that he is indeed very powerful. Satan is not omnipresent. He cannot be in more than one place at a time. He pretty much has to rely on his demons to do his work for him. Although he and his demons can’t read our minds, they can hear our speech and see our actions. They are also capable of influencing our thoughts. He and his demons have been observing and tempting humans for thousands of years. They’ve learned a few things about us from watching us constantly, and know how to trip our trigger in our (obvious to them) areas of weakness. As we can sometimes know what someone is thinking that we are around a lot, so can they. Even if they’re not spot-on with their assessment, they know how to use it to their advantage. They are experts in human behavior.
As believers, it is important to know our enemy. Be wise to his schemes. Know that he is a master of deception. Most importantly, know that with God’s help and the Holy Spirit’s power, we can fend off his lies. When a thought comes into our mind that is not in line with the Word of God, we are to “cast down imaginations and every high thing that exalts itself against the knowledge of God, and bring into captivity every thought to the obedience of Christ.” 2 Corinthians 10:5
Remember, just because he presented the thought/temptation, doesn’t mean you have to act upon it. It also doesn’t mean you have sinned, unless you choose to dwell on it. He realizes no success until he hears our words or sees our actions confirming his influence on our minds.