We do not deny the role of the Holy Spirit as a teacher. We believe that the Holy Spirit does serve to teach us, and to guide us. The Holy Spirit also serves to convict sinners that they may come to repentance.
From the article you linked to:
Consequently, sola scriptura demands that only those doctrines are to
be admitted or confessed that are found directly within or indirectly
by using valid logical deduction or valid deductive reasoning from
scripture. However, sola scriptura is not a denial of other
authorities governing Christian life and devotion. Rather, it simply
demands that all other authorities are subordinate to, and are to be
corrected by, the written word of God.
The problem lies in the fact that many false teachers have come into the world, and any of them can (and do) claim to have teachings from the Holy Spirit, from angels, from God the Father through divine revelation, or through personal encounters with Jesus Christ Himself. Likewise, our own hearts and thoughts are not trustworthy and can deceive us.(Jeremiah 17:9) The Bible warns us not to trust every spirit, but to test them to see if they are false or true. The test is simple.
1 John 4:1-6 (KJV)
1 Beloved, believe not every spirit, but try the spirits whether they
are of God: because many false prophets are gone out into the world.
2 Hereby know ye the Spirit of God: Every spirit that confesseth that
Jesus Christ is come in the flesh is of God: 3 And every spirit that
confesseth not that Jesus Christ is come in the flesh is not of God:
and this is that spirit of antichrist, whereof ye have heard that it
should come; and even now already is it in the world. 4 Ye are of God,
little children, and have overcome them: because greater is he that is
in you, than he that is in the world. 5 They are of the world:
therefore speak they of the world, and the world heareth them. 6 We are
of God: he that knoweth God heareth us; he that is not of God heareth
not us. Hereby know we the spirit of truth, and the spirit of error.
Based on this Scripture, as well as John 15:26, we believe that before believing the teaching of the Holy Spirit, we need to first test to ensure that what we perceive of as the Holy Spirit meets the test, and is the Holy Spirit. The test is found in Scripture, which is unchanging, and serves as a plumb-line to ensure that the teaching of the Holy Spirit lines up.
Therefore, the Holy Spirit cannot teach anything that is not in accordance with God's Word, whether explicitly or implicitly.